1. Field of the Invention
The present invention relates to a sheet stacking apparatus and a sheet stacking method, and more particularly relates to a sheet stacking apparatus which positions each of a plurality of sheets sequentially thrown in from a conveying device at a predetermined stacking position and stacks these sheets in layers; and a sheet stacking method using the sheet stacking apparatus.
2. Description of the Related Art
In a processing line of a planographic printing plate, a planographic printing sheet to which a protection sheet is attached is cut into a product size, and the like. Then, the planographic printing plate is placed on a conveying unit such as a belt conveyor, a roller conveyor, and the like, and conveyed, by the conveying unit, to a stacking apparatus of the planographic printing plate provided at the end of the processing line. The stacking apparatus is provided with, for example, a stacking platform for receiving the planographic printing plate thrown in above from the conveying unit; and a back member, a front member, and a pair of side members for positioning planographic printing plates sequentially thrown in onto the stacking platform at a predetermined stacking position respectively.
The back member is elastically supported by a coil spring or the like and is arranged so as to face the front end of the planographic printing plate on the stacking surface. When a planographic printing plate is thrown in from the conveying unit onto the stacking surface, the back member elastically receives the front end of the planographic printing plate which tries to move in the conveying direction by the inertia thereof, limits the movement of the planographic printing plate in the conveying direction, and urges the planographic printing plate in a direction opposite to the conveying direction as needed. In addition, the front member is arranged so as to face the back end of the planographic printing plate on the stacking surface, comes in contact with the planographic printing plate whose movement in the conveying direction is limited or which is urged in a direction opposite to the conveying direction by the back member, and positions the planographic printing plate along the longitudinal direction thereof.
A pair of side members is arranged so as to face each of the both ends of the planographic printing plate on the stacking surface. Each of the side members is formed of a plate material having enough high strength such as a thick steel plate. The pair of side members includes: an inclined guide surface which is provided at the upper side thereof, and is inclined with respect to the height direction; and a positioning surface which is provided at the lower side thereof, and is formed along the height direction. Therefore, the planographic printing plate stacked on the stacking platform is positioned near the center position between the pair of side members facing each other.
Accordingly, when the conveying unit sequentially throws in a plurality of planographic printing plates onto the stacking surface of the stacking apparatus, the planographic printing plates are positioned at predetermined stacking position on the stacking surface by the front member and the pair of side members and are stacked in layers. At this time, when the number of planographic printing plates on the stacking surface reaches a predetermined number for one stack bundle defined by a shipping specification and the like, the predetermined number of planographic printing plates are transshipped as a stack bundle from the stacking apparatus to a pallet or the like, and the bundle is conveyed to packaging and shipping processes or a storage warehouse or the like.
For example, Japanese Patent Application Laid-Open No. 2002-046924 discloses such a stacking apparatus that can align the side ends of planographic printing plates stacked on the stacking platform without causing the planographic printing plates to be stuck or deformed around side ends thereof, when the planographic printing plates are thrown in from the conveying device to the stacking platform. In the stacking apparatus, an elastic member can be elastically deformed along the width direction of the planographic printing plate and is supported so as to be in contact with the side end surface of the planographic printing plate thrown in from the conveying device. And, if the planographic printing plate thrown in from the conveying device is shifted away from a predetermined width position along the width direction, the elastic member urges the planographic printing plate to the predetermined width position side so as to position the planographic printing plate having been stacked on the stacking surface at the predetermined width position. In such a configuration of the back member of the stacking apparatus, the planographic printing plates sequentially thrown in from the conveying device can be positioned with good precision by the elastic member while the planographic printing plate is dropping onto the stacking surface or immediately after the planographic printing plate has been stacked on the stacking surface. Accordingly, a plurality of planographic printing plates thrown in from the conveying device can be stacked on the stacking surface such that the side ends of the planographic printing plate are matched with each other.